假设我们在表中有14条name列的记录

在小组由

select name,count(*) as totalcount from person where name='Please fill out' group BY name;

它将给出单行计数，即14

但是在除以

select row_number() over (partition by name) as total from person where name = 'Please fill out';

它将增加14行计数

分区并不会实际卷起数据。它允许您在每个组的基础上重置一些东西。例如，通过对分组字段进行分区并对组中的行使用rownum()，可以获得组中的序数列。这使您的行为有点像在每个组的开头重置的标识列。

-- BELOW IS A SAMPLE WHICH OUTLINES THE SIMPLE DIFFERENCES
-- READ IT AND THEN EXECUTE IT
-- THERE ARE THREE ROWS OF EACH COLOR INSERTED INTO THE TABLE
-- CREATE A database called testDB


-- use testDB
USE [TestDB]
GO


-- create Paints table
CREATE TABLE [dbo].[Paints](
    [Color] [varchar](50) NULL,
    [glossLevel] [varchar](50) NULL
) ON [PRIMARY]

GO


-- Populate Table
insert into paints (color, glossLevel)
select 'red', 'eggshell'
union
select 'red', 'glossy'
union
select 'red', 'flat'
union
select 'blue', 'eggshell'
union
select 'blue', 'glossy'
union
select 'blue', 'flat'
union
select 'orange', 'glossy'
union
select 'orange', 'flat'
union
select 'orange', 'eggshell'
union
select 'green', 'eggshell'
union
select 'green', 'glossy'
union
select 'green', 'flat'
union
select 'black', 'eggshell'
union
select 'black', 'glossy'
union
select 'black', 'flat'
union
select 'purple', 'eggshell'
union
select 'purple', 'glossy'
union
select 'purple', 'flat'
union
select 'salmon', 'eggshell'
union
select 'salmon', 'glossy'
union
select 'salmon', 'flat'


/*   COMPARE 'GROUP BY' color to 'OVER (PARTITION BY Color)'  */

-- GROUP BY Color 
-- row quantity defined by group by
-- aggregate (count(*)) defined by group by
select count(*) from paints
group by color

-- OVER (PARTITION BY... Color 
-- row quantity defined by main query
-- aggregate defined by OVER-PARTITION BY
select color
, glossLevel
, count(*) OVER (Partition by color)
from paints

/* COMPARE 'GROUP BY' color, glossLevel to 'OVER (PARTITION BY Color, GlossLevel)'  */

-- GROUP BY Color, GlossLevel
-- row quantity defined by GROUP BY
-- aggregate (count(*)) defined by GROUP BY
select count(*) from paints
group by color, glossLevel



-- Partition by Color, GlossLevel
-- row quantity defined by main query
-- aggregate (count(*)) defined by OVER-PARTITION BY
select color
, glossLevel
, count(*) OVER (Partition by color, glossLevel)
from paints

PARTITION BY是分析的，GROUP BY是聚合的。为了使用PARTITION BY，你必须用OVER子句来包含它。

假设我们在表中有14条name列的记录

在小组由

select name,count(*) as totalcount from person where name='Please fill out' group BY name;

它将给出单行计数，即14

但是在除以

select row_number() over (partition by name) as total from person where name = 'Please fill out';

它将增加14行计数

我们可以举一个简单的例子。

考虑一个名为TableA的表，其值如下:

id  firstname                   lastname                    Mark
-------------------------------------------------------------------
1   arun                        prasanth                    40
2   ann                         antony                      45
3   sruthy                      abc                         41
6   new                         abc                         47
1   arun                        prasanth                    45
1   arun                        prasanth                    49
2   ann                         antony                      49

集团

可以在SELECT语句中使用SQL GROUP BY子句进行收集 跨多个记录的数据，并将结果按一个或多个分组 列。 简单来说，GROUP BY语句与 聚合函数将结果集按一个或多个分组 列。

语法:

SELECT expression1, expression2, ... expression_n, 
       aggregate_function (aggregate_expression)
FROM tables
WHERE conditions
GROUP BY expression1, expression2, ... expression_n;

我们可以在我们的表中应用GROUP BY:

select SUM(Mark)marksum,firstname from TableA
group by id,firstName

结果:

marksum  firstname
----------------
94      ann                      
134     arun                     
47      new                      
41      sruthy   

在我们的实际表中，我们有7行，当我们应用GROUP BY id时，服务器会根据id对结果进行分组:

简单地说:

这里GROUP BY通常减少滚动返回的行数 并为每一行计算Sum()。

分区的

在讨论PARTITION BY之前，让我们看一下OVER子句:

根据MSDN的定义:

控件中定义窗口或用户指定的行集 查询结果集。然后，窗口函数为每一行计算一个值 在窗户里。可以对函数使用OVER子句进行计算 诸如移动平均线、累计总数、 运行总数，或每组结果的前N名。

PARTITION BY不会减少返回的行数。

我们可以在示例表中应用PARTITION BY:

SELECT SUM(Mark) OVER (PARTITION BY id) AS marksum, firstname FROM TableA

结果:

marksum firstname 
-------------------
134     arun                     
134     arun                     
134     arun                     
94      ann                      
94      ann                      
41      sruthy                   
47      new  

看看结果——它将对行进行分区并返回所有行，这与GROUP BY不同。